A conventional DC motor is shown in FIGS. 1 through 7B, among which FIGS. 1 through 4 illustrate the detailed construction and method of assembling the motor, and FIGS. 5 through 7A illustrate the detailed construction and method of assembling the armature section B in the same motor.
More specifically, FIG. 1 is a partially exploded perspective view of a conventional DC motor made up of a rotor (not shown) having a rotating shaft, a bearing 60, an armature section B composed of a hollow stator 70 and a circuit board 80, and a stator base 90. The bearing 60 has a central bore 61 that serves to rotatably support the rotating shaft of the rotor.
The circuit board 80 includes a motor control circuit (not shown) electrically connected to the winding of stator described below to control the operation of the motor, and a central hole 81 (see FIG. 5).
Referring to FIGS. 1, 6, and 7A, the stator 70 comprises a hollow set 71 of silicon steel sheets composed of plural stacked silicon steel sheets, a winding (denoted by a character W in FIG. 7B) adapted to generate a magnetic field required by the motor; a hollow cylindrical isolation bushing 72 adapted to separate and thus to isolate the silicon steel sheets set 71 and the winding, and plural positioning feet 73.
FIGS. 6, 7A, 7B illustrate the method of assembling the armature section B in the motor shown in FIG. 1. Specifically, FIG. 6 is a cutaway perspective view, FIG. 7A an enlarged fragmentary view of a "Y" part of FIG. 6, and FIG. 7B a further enlarged sectional view of a the vicinity of "Y" part illustrated upside down relative to with FIGS. 6 and 7A.
As shown in FIG. 7B, the afore-mentioned winding W is provided between the isolation bushing 72 and the plural positioning feet 73 of stator 70. For attaching the circuit board 80 to the stator 70 to form the armature section B (FIG. 1), the circuit board 80 is first laid over the positioning feet 73 and the lower end 72L of the isolation bushing 72, a positioning pin P is inserted into a hole provided in each locating foot 73, and one terminal portion of the winding W is wound around the post P. In the above situation, the circuit board 80, stator 70, and winding W together are moved through a tin bath (not shown) so as to solder the circuit board 80 to the stator 70 by means of the tin solder Q adhering to the circuit board 80 over the post P.
A drawback of the aforementioned assembly method of armature section B is explained below. While performing the soldering operation in the tin bath, if the clearance between the circuit board 80 and the lower end 72L of isolation bushing 72 is not uniform or if vibration occurs, positioning between the stator 70 and the circuit board 80 is apt to shift, thus resulting in warp or tilt of circuit board 80 in the armature section B.
As shown in FIG. 1 to FIG. 4, stator base 90 includes a base N adapted to receive circuit board 80; and a substantially cylindrical hollow hub M integrally formed in the central portion of the base N. The hub M includes a substantially cylindrical upper part 91; a substantially cylindrical lower part 92 slightly larger in its outer diameter than upper part 91; and a step portion 93 interconnecting the upper part 91 and the lower part 92. Referring to FIG. 1, before assembling the armature section B onto the stator base 90, glue is first applied onto the outer surface 94 of upper part 91, and then the hub M of stator base 90 is inserted through the hollow silicon steel sheets set 71 and the hollow isolation bushing 72 of stator 70 (see FIGS. 2 and 3), with the silicon steel sheets set 71 being in close contact with the outer surface of upper part 91 on its inner surface, and being supported by the step portion 93 at its bottom, so as to bond the stator 70 to the stator base 90 by glue. A central hole 95 adapted to rotatably support a bearing 60 is provided in the hub M. FIG. 4 shows the condition wherein the bearing 60 is fitted in the central hole 95.
The aforementioned structure of stator base 90 has the following drawbacks. First, since silicon steel sheets set 71 is bonded to the outer surface 94 of hub M by glue which tends to deteriorate under high temperature and of which properly applied quantity can hardly be attained, sufficient bonding strength between stator 70 and stator base 90 cannot be guaranteed, and thus relative displacement in circumferential and axial directions between stator 70 and stator base 90 cannot be effectively avoided. Besides, since no engaging mechanism for the bearing 60 is provided within the central hole 95 of stator base 90 (see FIG. 4), bearing 60 is fitted into central hole 95 by a force fit for positioning it. However, if the fit is too tight, the fitting of rotor shaft into the central bore 61 of bearing 60 will be difficult. On the other hand, if the fit is too loose, it will be very difficult to prevent the displacement of bearing 60 within the central hole 95.
In view of above, the primary object of the present invention is to provide an improved motor structure in which circumferential and axial displacement of the stator relative to the stator base can be positively stopped without using glue, and the yield rate and reliability of produced motors can be greatly improved.
Another object of the present invention is to provide an improved motor structure in which the bearing of the rotor shaft can be reliably located at a fixed position in a central hole of the stator base without using force fitting, and the yield rate and reliability of produced motors can be greatly improved.
Yet another object of the present invention is to provide an improved motor structure in which the circuit board can be firmly held together with the stator so as to prevent relative vibration or uneven clearance between the circuit board and the lower end of stator upon performing a soldering operation in the tin bath, and thus avoid warp or tilt of circuit board in the armature section. Consequently, the yield rate and reliability of produced motors can be greatly improved.